Optimization of mud cleanup for openhole horizontal wells

Successful completion of openhole horizontal wells requires removal of pote ntial impairment from the near wellbore and formation face. Impairment can reduce well productivity and lead to failure of sand control screens due to plugging and erosion. Shell has adopted the practice in the Gulf of Mexico of employing drill-in fluids with acid-soluble bridging and weighting agen ts for all openhole drilling and extensive displacement and acid cleanup pr ocedures during horizontal well completions. Drill-in fluid and filtercakes are removed with specially formulated sweeps and by attainment of sufficie nt velocity to achieve effective displacement. Filtercakes are removed with specially formulated washes applied using washcups or coil tubing to ensur e that the cleanup formulations contact the filtercake materials. Drill-in fluids and cleanup systems must be specially formulated and evalua ted for specific applications. We have adopted a suite of laboratory screen ing tests to evaluate formation damage and removal chemistries to ensure th at each well is effectively cleaned. These tests can also be used to evalua te new fluid systems before taking them to the field. Our approach in this instance is to compare data from new fluids to results obtained with fluids with which we have a Successful field track record. In this article we wil l review these procedures and the results with a variety of fluid systems.